1. Field of Invention
This invention relates to a semiconductor device, and more particularly relates to a metal-oxide-semiconductor (MOS) transistor.
2. Description of Related Art
It is important in the semiconductor technology to reduce feature sizes, improve the speed and the cost per integrated circuit unit, and so on. With the development of semiconductor technology, high-power devices have been applied to various electronic products in different fields. The laterally diffused MOS (LDMOS) or extended-drain MOS (EDMOS) transistor is widely used in high-voltage or high-power PMIC (power management integrated circuit) application as the driving device.
In consideration of power consumption, the On-resistance (Ron) is an important characteristic for PMIC products, especially for portable IC devices. The Ron can be effectively decreased by modifying the structure of the LDMOS or EDMOS device, e.g., changing the shape of the isolation (e.g., STI) or a doping well, but Ron improvement is still limited on current LDMOS or EDMOS devices. Also, increasing the breakdown voltage (BVD) is important for performance of LDMOS or EDMOS devices.